A fuel cell is an electrochemical device that includes an anode and a cathode with an electrolyte disposed therebetween. The anode receives a fuel such as hydrogen gas and the cathode receives an oxidant such as oxygen or air. Typically, a main hydrogen passage provides communication between a source of hydrogen and the anode. Several fuel cells are combined in a fuel cell stack to generate a desired amount of electrical power. A fuel cell stack for a vehicle may include several hundred individual cells.
Oxygen not consumed in the fuel cell stack is expelled as a cathode exhaust gas that may include water as a stack by-product. Hydrogen not consumed in the stack may be recirculated to the main hydrogen passage via a fuel recirculation passage. An amount of undesirable nitrogen is also present in the unused hydrogen exiting the fuel cell. Before reintroducing the unused hydrogen back into the main hydrogen passage, a portion of the hydrogen/nitrogen mixture is exhausted into the atmosphere. This can be accomplished by a bleed valve, for example. Hydrogen and nitrogen that are not exhausted into the atmosphere through the bleed valve can be reintroduced to the main hydrogen supply via the fuel recirculation passage. The fuel recirculation passage provides fluid communication between the outlet of the fuel cell and the main hydrogen passage to allow unused hydrogen to be reintroduced to the anode. In fuel cell stacks of the prior art, an electric pump is used to recirculate the hydrogen/nitrogen mixture back into the main hydrogen passage.
It has been a continuing challenge to provide an efficient and cost effective method of reintroducing the unused hydrogen back into the main hydrogen passage. Space in and around the fuel cell stack is extremely limited and valued, especially in vehicular applications. Further, the electric pump used to reintroduce the unused hydrogen back into the main hydrogen passage utilizes electrical power generated by the fuel cell stack, thereby decreasing overall efficiency.
To reduce a power consumption of the electric pump, pulsed injectors which alternate between an open and closed position have been used in fuel cell systems to introduce fuel from the fuel source to the fuel cell stack. While pulsed injectors have been successful at reducing the power consumption of the electric pump, there is a need to minimize the time the injector is closed and maximize the time the ejector is used at low power.
It would be desirable to produce a fuel cell stack assembly including an array of injectors and ejectors that support hydrogen recirculation and maximize the use thereof, wherein the use of an electric pump is eliminated.